The present invention relates to a cell search method in a wireless communication system, and more particularly, to a cell search method capable of reducing the computational complexity for Secondary Synchronization Signal (SSS) detection by selecting a sequence group of which a cross-correlation between SSS sequences is a predetermined value or more, and then performing cell search only within the sequence group during the SSS detection for searching a cell group ID in 3GPP LTE communication.
Recently, the 3rd Generation Partnership Project (3GPP), which is a W-CDMA Organizational Partner, is conducting research on Long Term Evolution (LTE) as a relay technology of the 4th Generation wireless communication which can be a successor of W-CDMA or HSPDA.
As wireless access technology of the LTE system, Orthogonal Frequency Division Multiple Access (OFDM) has been adopted for the downlink, and Single-Carrier Frequency Division Multiple Access (SC-FDMA) has been adopted for the uplink.
OFDM is a transmission technique for dividing frequency bands into plural subcarriers and transmitting data through each subcarrier. This technique assigns subcarriers closely so as to partially overlap with each other in the frequency domain without interfering with each other, thereby realizing high-speed transmission and improving the utilization efficiency of frequency.
SC-FDMA is a transmission technique for dividing a frequency band and transmitting data through different frequency bands between plural terminals, thus making it possible to reduce interference between the terminals. This technique can realize low power consumption and wide coverage of a terminal because this technique has the characteristic that the variation in transmission power is small.
Also, in order to reduce the effect of inter-symbol interference caused by a slow wave in OFDM, LTE has two types of Cyclic Prefixes (CPs) having different lengths, of which one is a normal CP and the other is an extended CP. For example, the extended CP is applied to large-radius cells and transmission of Multimedia Broadcast Multicast Service (MBMS) signals, but the normal CP is applied to small-radius cells.
Generally, in a wireless communication system using W-CDMA, LTE, or the like, a mobile station should perform cell search which is an operation of finding out a cell with good wireless quality and setting up wireless link in order to establish communication environment with a base station based on synchronization signals during power-on, standby, communication, or intermittent reception under communication.
The above-described technology means the background in the art to which the present invention pertains, but does not mean the prior art.
In a cell search method in an LTE communication, cell search is performed by using Primary Synchronization Signal (PSS) sequence and Secondary Synchronization Signal (SSS) sequence.
An LTE system identifies a total of 504 cells because there are 168 cell group IDs each of which includes three cell IDs, wherein the PSS sequence identifies three cell IDs and the SSS sequence identifies 168 cell group IDs. Therefore, the LTE system may perform synchronization and cell search using these two signals.
First, by using the cross-correlation between the PSS sequence transmitted through frames and a known PSS sequence, the LTE system estimates symbol timing and frequency synchronization, and then obtains cell IDs in a cell group ID.
Thereafter, the LTE system finds out the SSS sequence having the highest cross-correlation using cross-correlations between the SSS sequence transmitted through frames and all of 168 known SSS sequences, and then detects frame boundaries and cell group IDs.
However, the aforesaid method has a problem in that applying cross-correlations to all occasions leads to an increase in computational complexity at a receiver because there are 168 types of SSS sequences each of which is comprised of a sequence of length 62 symbols.